This invention relates to an optical information storage material, and more particularly pertains to the such material which can assume two or more physical states, each of which have different optical densities.
Amorphous materials have hitherto fallen into one of the above-mentioned categories. The state of these amorphous materials can be changed by applying electrical, optical, or thermal energy thereto. In one state such material has a so-called non-crystalline bulk structure which has partial order of the atoms and molecules when viewed microscopically but is seen to have a non-crystalline structure and low optical density. In the other state the material has a crystalline structure which has relatively high optical density. By utilizing such optical properties, i.e., the change of state from low optical density to high optical density or a reverse change thereof, the amorphous materials have been able to function as an optical information storage device when used in the form of a thin film.
Amorphous materials which have been utilized in an optical information storage device were multi-component materials such as (Te, Ge, Sb, S) or (Te, Ge, As, Ga).
The hitherto known materials described above are chalcogenide composites which easily form a two dimensionally bonded atomic configuration in a glassy state, or are composites which are obtained by adding elements which easily form a covalent tetrahedral atomic structure with the chalocogenide composites.
Those composites are superior in that both crystalline and non-crystalline states thereof are stable at room temperature.
With respect to optical sensitivity, however, those composites have insufficient sensitivity for the use in optical information storage.
Furthermore thin films consisting of those composites have a relatively high optical density in the non-crystalline state.
Therefore, when making record on a film with a thickness capable of giving a high contrast ratio (e.g. &gt; 10 : 1), read-out-efficiency is relatively low i.e. &lt; 10%.